1. Field of the Invention
This invention relates to closure means for well conduits. More particularly, it relates to temporary plugs that are removable without mechanical intervention from the surface above the well.
2. Description of the Related Art
In conventional practice, when a well conduit is desired to be temporarily closed off, it is common to set a plug within the conduit to preclude the flow of fluids at the preferred location. Regarding oil and gas wells, there are may types of plugs that are used for different applications. As an example, there are known removable plugs typically used during cementing procedures that are made of soft metals that may be drilled out of the conduit after use. Plugs that may be removed from a well intact are referred to as "retrievable" plugs. Removal, however, requires mechanical intervention from the surface of the well. Common intervention techniques include re-entry into the well with wireline, coiled tubing, or tubing string.
After a conventional type plug has been set and it subsequently becomes necessary to reestablish flow, any tools that have been associated with the plug during its use must be removed or "pulled" from the well to provide access to the plug for the removal process. The pulling of tools and removal of the plug to reestablish flow within a downhole conduit often entails significant cost and rig downtime. It is, therefore, desirable to develop a plug which may be readily removed or destroyed without either significant expense or rig downtime.
Known conduit plugs incorporating frangible elements that must be broken from their plugging positions include frangible disks that are stationarily located within tubular housings and flapper type elements. Breakage may be initiated by piercing the plug to cause destructive stresses within the plug's body, mechanically impacting and shattering the plug, or increasing the pressure differential across the plug until the plug is "blown" from its seat. After breakage has occurred, the resulting shards or pieces must be washed out of the well bore with completion fluid or the like in many situations. Because most known designs call for a relatively flat plug to be supported about its periphery, the plug commonly breaks from the interior outwardly and into relatively large pieces.
In some cases, operations within a well will require that a temporary plug be set within a conduit, usually the tubing string or well casing, but it may also be tubular components associated with downhole tools being used in the well. An example of such a downhole tool is a pressure set packer. In a typical configuration, the packer assembly will have a tail-pipe extending below the pack off elements. A temporary plug will have been installed in the tail-pipe before the packer is placed within the well or will be installed during the setting process. Frangible plugs described hereinabove may be used to plug the tail-pipe. Alternative plug means may include a wireline disposed plug, a wireline disposed dart, or a seated ball. In any event, after the packer has been set, it is desirable that the plugging structure be removed in order to establish a passage way through the packer assembly. As previously described, a frangible plug in the packer must be mechanically broken from its seat. In the case of a ball seated in a collet catcher sub, sufficient pressure must be applied above the packer to expel the ball into the well beyond the packer assembly.
A common detriment of either the destroyed frangible member or the expelled ball is that potentially fouling debris remains in the well. The debris' significance increases in non-vertical wells because it may remain relatively localized at the location of dislodgment where continuing well activity and operations may take place, or at least pass in the future. The debris may also be carried upward in the well fouling equipment along the way or surface equipment at the top of the well. This should be contrasted to vertical wells where the debris is more likely to fall clear of working mechanisms, but may also create fouling problems.